1. Field of the Invention
This invention relates generally to a system comprising an implantable electrical medical device such as a cardiac pacemaker, together with an external device that provides a bidirectional telemetric link to the implantable medical device. This invention relates in particular to the functionality of such an external patient device. The patient device comprises a receiver, a memory operatively connected to the receiver, the memory being configured to store code identifying a specific implant (implant's identification code (IID)), a timer and, a control unit operatively connected to the receiver, the memory and the timer.
2. Description of the Related Art
In a system comprising one or more implantable medical devices (IP) and one or more patient devices (PD, also referred to as external device), an implantable medical device and patient device may include transceivers that facilitate bidirectional communications between the devices for home monitoring purposes. For wireless communication in such environment the MICS (Medical Implant Communications Service) frequency band is reserved.
In a system for bidirectional communication each patient device should be assigned to a single implant to prevent multiple patient devices from attempting communication with a single implant. This is particularly important in an area where multiple patient devices are in close proximity (e.g., in a nursing home), and so competition between patient devices may result in failed communications due to interference.
If unidirectional telemetry (i.e. telemetry from implant to patient device) is used, then such assignment is not necessary, as unidirectional telemetry does not require or provide for acknowledgements.
In order to follow the MICS regulations as defined by the FCC and ETSI, when communications are to be established, it is necessary for the patient device to scan the MICS band, to find the Least Interfered-with Channel (LIC), and then to transmit a beacon signal to the implant. Subsequently, the implant must search the band to find the channel on which the patient device is transmitting, and only then may the implant use that channel to transmit its data to the patient device. If periodic communications are desired, time synchrony of the implant and patient device is needed in order to prevent either unnecessary emission by the patient device on the MICS band, or unnecessary receiver activity (thus power consumption by the implant) outside of the time of interest. Therefore, timing information is exchanged between the implant and patient device during their communications.
Presently, assignment is achieved manually by addressing the patient device via the internet and transmitting an implant identification code to the patient device to thus assign the patient device to the implant specified by the implant identification code.